This invention relates to liquid, hydrophobic, non-migrating, non-functional polyurethane plasticizers. It is also directed to a process for the production of these plasticizers, a process for the production of a polyurethane comprising the reaction between an isocyanate component and an isocyanate-=reactive component in the presence of these plasticizers, and to the polyurethanes produced by that process.
Plasticizers are generally used in plastics (i.e., PVC) to adjust hardness, flexibility and processing characteristics. Plasticizers are also used in commercial polyurethane elastomer formulations to provide products exhibiting higher flexibility, lower hardness, and lower rebound resulting in increased energy absorption. However, these products can potentially embrittle over time due to migration of the plasticizer. Plasticizers that have a minimal effect on hardness and physical properties, and which are non-migrating are desirable for polyurethane elastomers prepared by a one-shot cast elastomer process.
Diurethanes are known and described as suitable stabilizing additives for sealing compounds, in, for example, U.S. Pat. No. 4,824,888 and as plasticizers for polyurethane based sealing and adhesive compositions in U.S. Pat. No. 5,525,654.
U.S. Pat. No. 4,824,888 discloses diurethanes which correspond to one of two general formulas, which are useful as stabilizing additives in sealing compounds based on isocyanate-terminated prepolymers of difunctional and trifunctional polyether or polyester polyols and/or polyvinylchloride swellable copolymers of vinyl chloride with monomers from the group vinyl acetate, vinyl propionate and alkyl acrylates. These diurethanes are reaction products of monofunctional alcohols and diisocyanates. In particular, the monoalcohols are monofunctional polypropylene glycol monoalkyl ethers having a molecular weight of about 500 to 2000. These diurethanes are also suitable stabilizing agents for isocyanate-terminated polyurethane prepolymers, and for polyvinyl chloride homopolymer or copolymer plastisols.
Moisture curing sealing and/or adhesive compositions based on alkoxysilane-terminated polyurethanes which contain diurethanes as plasticizers are described by U.S. Pat. No. 5,525,654. These diurethanes are prepared from either diol mixtures and monofunctional isocyanates wherein substantially all the free hydroxyl groups are reacted, or from diisocyanates and monofunctional alcohols wherein substantially all the free isocyanate groups are reacted.
Other urethane plasticizers are disclosed in, for example, U.S. Pat. Nos. 4,123,413 and 4,482,408. The urethane plasticizers of U.S. Pat. No. 4,123,413 correspond to one of three general formulas, and are prepared by reaction of an alcohol or a phenol with an isocyanate, from amines and chloroformates, or from chloroformamides and alcohols or phenols in the presence of acid binding agents.
The urethane plasticizer of U.S. Pat. No. 4,482,408 is octyldecylbutyl urethane and is prepared by reacting an equimolar mixture of octyldecyl isocyanate and n-butyl alcohol. This urethane plasticizer is a mono-urethane described as a straight-chain, saturated, carbamic acid ester and is suitable as a plasticizer for propellant compositions with problems of plasticizer migration which typically occur during propellant storage.
Useful polyurethane plasticizers according to the present invention are based on isocyanate-terminated prepolymers reacted with monoalcohols or mixtures of monoalcohols. They are prepared by either adding the alcohols to the prepolymer or by addition of the prepolymer to the monofunctional alcohol(s). Most hydrophobic, non-functional polyurethane plasticizers are viscous liquids at 25xc2x0 C. but usually exhibit viscosities of less than about 100,000 mPaxc2x7s at 50xc2x0 C. The resulting polyurethanes do not contain any free hydroxyl- or isocyanate-groups, and thus they are non-reactive and can be added to either isocyanates or polyols to form stable mixtures.
The use of these polyurethane plasticizers in one-shot polyurethane elastomers has several important benefits:
1) Addition to either the polyol or the isocyanate composition allows one to adjust the mix ratio very favorably, i.e., to adjust a 1:1.5 ratio to an easier to process ratio of 1:1.
2) Addition to either the polyol or the isocyanate compositions allows one to adjust the viscosities of the two components very favorably, i.e., to obtain viscosities which are similar which facilitates the mixing process.
3) Unmodified polyisocyanates that contain no urethane, allophanate, urea, or biuret groups are usually very incompatible with polyol compositions due to major differences in surface energy (i.e., polarity). Addition of the diurethane containing plasticizers according to the invention to either the polyisocyanate or both the polyisocyanate and polyol side of one-shot elastomer formulations helps to overcome these incompatibility problems and thus facilitates mixing.
Although it is possible in one-shot elastomer formulations to meter the single components separately and mix them, i.e., in a reactor or mixhead, it is preferred to combine the liquid, hydrophobic, polyurethane containing plasticizer with the polyisocyanate and/or the polyol/chain extender blend (or individual components) prior to mixing the isocyanate containing the isocyanate reactive polyol components.
Besides the processing advantages polyurethane plasticizers provide in one-shot polyurethane elastomer formulations, they do not show any substantial migration or lower the physical properties of the final polyurethane elastomer upon aging to the extent observed in state of the art non-urethane group containing plasticizers. As a result, the high performance properties of one-shot polyurethane elastomers are effected minorly when polyurethane containing plasticizers are used in the formulation.
This invention relates to liquid, hydrophobic, non-migrating, non-functional polyurethane plasticizers having a viscosity of less than about 100,000 mPaxc2x7s, preferably less than about 20,000, at 50xc2x0 C. These plasticizers comprise the reaction product of (1) an isocyanate-terminated hydrophobic prepolymer having an NCO group content of less than 20%, and (2) a monofunctional alcohol having a molecular weight of about 32 to about 1,000, preferably of about 128 to about 720, most preferably about 128 to about 300, and an OH number of about 56 to about 1750, preferably of about 78 to about 438, most preferably of about 187 to about 438; wherein components (1) and (2) are present in equivalent ratios to form the resultant liquid, hydrophobic polyurethane plasticizers. The resultant plasticizers have a ratio of carbon atoms to oxygen atoms of at least 6:1, preferably of at least 7:1, and most preferably of at least 8:1.
As used herein, the phrase liquid, hydrophobic, non-migrating, non-functional, polyurethane plasticizers refers to liquid polyurethane oligomers having a carbon to oxygen ratio of at least 6:1, which lack the affinity to absorb water, and do not have any functional groups to react with isocyanates or polyols (i.e. do not contain free isocyanate groups or Zerewittinov active hydrogens). The polyurethane oligomers have average molecular weights in the range of from about 500 to about 3,000, preferably about 600 to about 1,500.
Suitable (1) hydrophobic isocyanate-terminated prepolymers comprise the reaction product of (a) a diisocyanate component having an NCO group content of about 25.0% to about 60.0%, preferably of about 32% to about 50%, and a functionality of about 2.0; with (b) at least one hydrophobic polyol having a molecular weight of about 200 to about 4,000, preferably of about 400 to about 2,000, an OH number of about 28 to about 561, preferably about 56 to about 280, and a functionality of from about 1.8 to about 3.0, preferably about 2.0 to about 2.2, and wherein the hydrophobic polyol contains only carbon atoms in the backbone of the molecule. The relative amounts of diisocyanate and hydrophobic polyol are such that the NCO:OH equivalent ratio is from about 2:1 to about 7:1, and preferably from about 3:1 to about 5:1.
This invention also relates to a process for the production of these liquid, hydrophobic, non-migrating, non-functional polyurethane plasticizers that are characterized by a viscosity of less than about 100,000 mPaxc2x7s (preferably less than about 20,000 mPaxc2x7s) at 50xc2x0 C. This process comprises:
(1) reacting
(a) a diisocyanate component having an NCO group content of about 25.0% to about 60.0%, preferably of about 32% to about 50%, and a functionality of about 2.0,
with
(b) at least one hydrophobic polyol having a molecular weight of about 200 to about 4,000, preferably of about 400 to about 2,000, an OH number of about 28 to about 561, preferably of about 56 to about 280, and a functionality of from about 1.8 to about 3.0, preferably about 2.0 to about 2.2, and which contains only carbon atoms in the backbone of the molecule;
at an NCO:OH equivalent ratio of from about 2:1 to about 7:1 to form an isocyanate-terminated prepolymer having an NCO group content of less than about 20%;
and
(2) reacting the isocyanate-terminated prepolymer formed in (1) above with
(c) a monofunctional alcohol having a molecular weight of about 32 to about 1,000, preferably of about 128 to about 720, and an OH number of about 56 to about 1750, preferably of about 78 to about 438.
This present invention also relates to a process for the production of a polyurethane, comprising reacting a polyisocyanate component with an isocyanate-reactive component in the presence of these liquid, hydrophobic, non-migrating, non-functional polyurethane plasticizers, as well as to the polyurethanes produced by this process.